The present invention relates generally to plant genetic engineering, and specifically to a novel gene useful for producing genetically engineered plants characterized as having a phenotype of increased crop yield.
Plant growth and development are governed by complex interactions between environmental signals and internal factors. Light regulates many developmental processes throughout the plant life cycle, from seed germination to floral induction (Chory, J. Trends Genet., 9:167, 1993; McNellis and Deng, Plant Cell, 7:1749, 1995), and causes profound morphological changes in young seedlings. In the presence of light, hypocotyl growth is inhibited, cotyledons expand, leaves develop, chloroplasts differentiate, chlorophylls are produced, and many light-inducible genes are coordinately expressed. It has been suggested that plant hormones, which are known to affect the division, elongation, and differentiation of cells, are directly involved in the response of plants to light signals (P. J. Davies, Plant Hormones: Physiology, Biochemistry and Molecular Biology, pp 1-836 , 1995; Greef and Freddericq, Photomorphogenesis, pp 401-427, 1983). The interactions between phototransduction pathways and plant hormones however are not well understood.
The brassinosteroids are a unique class of biologically active natural products that possess high specific activity and plant steroidal hormone activity. Their low effective concentrations for use on crops make them environmentally safe and those brassinosteroids used on a large scale are generally non-toxic. At the physiological level, brassinosteroids elicit many changes and could represent a new class of hormones in plants. The economic aspects of the brassinosteroids may have worldwide effects. The brassinosteroids can be used as plant protectants from both pesticide and environmental adversity. In addition, brassinosteroids appear to be important for insect control. Further, brassinosteroids may regulate some stage of the reproductive cycle in plants, and other species, thereby providing the means to increase or decrease the reproductive process. For example, in certain horticultural crops, it may be desirable to eliminate the flowering process to ensure continuous production of other tissues such as leaves, bulbs and other storage organs. This modulation of the reproductive process could be important in the control of certain seed bearing weeds, where cessation of the flowering cycle eliminates proceeding generations. Brassinosteroids also appear to stimulate root growth, and external application causes no deformity of plants.
Brassinosteroids qualify for classification as biochemical pesticides. Such pesticides are generally distinguished from conventional chemical pesticides by their unique modes of action, low effective concentration, target species, and specificity. Historically, the brassinosteroids have not been used in actual agricultural applications due to the expense involved in producing them as well as the difficulty in purifying them.
Although steroid hormones are important for animal development, the physiological role of plant steroids is largely unknown. The present invention is based on the discovery of the DET2 gene, which encodes a protein that shares significant sequence identity with mammalian steroid 5xcex1-reductases and is involved in the brassinolide biosynthetic pathway. A mutation of glutamate 204, which is required for the activity of human steroid reductase, abolishes the in vivo activity of DET2 and leads to defects in light-regulated development. These defects can be ameliorated by application of the plant steroid, brassinolide.
One embodiment of the invention provides DET2 polypeptide and isolated polynucleotide sequences encoding DET2.
Another embodiment of the invention provides antibodies that bind to the DET2 polypeptide.